* Five more states joining suit, which will now group 18
* Challenge says healthcare overhaul is unconstitutional
* Fla. attorney general says will pursue to Supreme Court (Adds healthcare analyst's comment)
By Pascal Fletcher
MIAMI, April 7 (Reuters) - Five more U.S. states are joining a Florida-led group of states in a lawsuit challenging President Barack Obama's overhaul of the U.S. healthcare system, Florida's attorney general said on Wednesday.
The joint lawsuit led by Florida and now grouping 18 states was filed on March 23 by mostly Republican attorney generals.
It claims the sweeping reform of the $2.5 trillion U.S. healthcare system, pushed through by Democrats in the U.S. Congress after months of bitter partisan fighting, violates state-government rights in the U.S. Constitution and will force massive new spending on hard-pressed state governments.
While some legal scholars think the suits will reach the Supreme Court, many agree that the supremacy clause of the Constitution, which puts the powers of the U.S. government above those of the states, will trump the states' arguments.
"We welcome the partnership of Indiana, North Dakota, Mississippi, Nevada and Arizona as we continue fighting to protect the constitutional rights of American citizens and the sovereignty of our states," Florida Attorney General Bill McCollum said.
He is seeking the Republican nomination to run for Florida governor.
South Carolina, Nebraska, Texas, Utah, Louisiana, Alabama, Colorado, Michigan, Pennsylvania, Washington, Idaho, and South Dakota had previously joined Florida's lawsuit.
All of these states' attorneys general are Republicans, except for Louisiana, where the post is held by a Democrat.
Another state, Virginia, has filed a separate suit, arguing the new law's requirements that most Americans buy health insurance clash with a state law that exempts Virginians from federal fines to be imposed for not owning health insurance.
The filings have touched off political debates in many states on whether the U.S. government should be sued.
The Justice Department, which is responsible for defending U.S. law in court, has said in response to the March 23 filing that it will vigorously fight any challenges to the new healthcare law, which it insists is constitutional. The White House has also said it believes the suits will fail.
Analysts at the Harvard School of Public Health predicted partisan politics would not only complicate implementation of healthcare reform, but also make it an influential factor in the congressional elections in November.
"While the bill has been signed into law, the critical details of its implementation are far from fixed," said HSPH's Robert J. Blendon, Professor of Health Policy and Political Analysis, citing a study of opinion polls on the health issue.
"Partisan differences in views about what should happen to this law remain so great that a Republican victory in either House could change the direction of the current reforms," Blendon said in a statement.
While many potential voters wanted the law to be scaled back, many others wanted the law changed to expand government's future role, the HSPH study found.
The Florida-led lawsuit says the health overhaul -- which expands government health plans for the poor, imposes new taxes on the wealthy and requires insurers to cover people with preexisting medical conditions -- violates the Constitution's commerce clause by requiring nearly all Americans to buy health insurance.
"On behalf of the residents in Florida and the states joining our efforts, we are committed to aggressively pursuing this lawsuit to the U.S. Supreme Court if necessary to prevent this unprecedented expansion of federal powers, impact upon state sovereignty, and encroachment on our freedom," McCollum said in a statement released by his office.
When he announced the joint lawsuit last month, McCollum said the healthcare reforms would add $1.6 billion to Florida's spending on the Medicaid health program for the poor.
Beyond raising Medicaid costs for Florida, McCollum argued in the 22-page lawsuit that the healthcare reforms added up to an unconstitutional power grab by the federal government that would force broad reorganization of state governments and massive hirings in order to comply with the new law.
The lawsuit asks the trial court to declare that the federal government is violating the sovereignty of the states and to bar federal agencies from enforcing the new law.
A scheduling hearing is set for April 14, 2010, at the federal courthouse in Pensacola. (For graphic on healthcare, click: link.reuters.com/xev76j) (Additional reporting by Maggie Fox in Washington, Editing by Tom Brown and Jackie Frank)